1. Field of the Invention
The present invention relates to a bearing assembly, and more particularly to an improvement in a bearing assembly capable of detecting the rotation of a rotary member integral with an outer ring.
2. Related Background Art
Bearing assemblies are employed for supporting rotating parts in various machines, and it often becomes necessary to detect the rotation of such rotating part. A typical example is found in an anti-skid braking system for a vehicle, in which the rotation of a wheel is detected and the braking action is temporarily released when the wheel approaches a locking state, thus preventing the wheel locking phenomenon. The rotation can be conveniently detected by a sensor utilizing a pulser gear or a sensor rotor fixed to the outer ring and an electromagnetic pickup.
Conventionally the pulser gear is composed of an annular member of a magnetic material, having gear teeth on the outer periphery, and said annular member is fitted on the outer periphery of the outer ring. The gear teeth have to be made by broaching, by mechanical working with a gear cutter, or by sintering. However, broaching or other mechanical working requires a high cost, while sintering cannot provide a sufficient strength and cannot be easily made rust-proof.
Also the pulser gear is obtained by forming plural projections in the radial direction with a constant interval, on the outer periphery of an annular member composed for example of a plate member of a magnetic material. The surface of the annular member is usually subjected to antirusting treatment, but the rotating ring is not subjected to such treatment. Consequently, the pulser gear and the rotating ring constitute a direct contact of different metals, which induces rusting in the pulser gear due to electric erosion if they are exposed, for example, to rain or water. Such rusting reduces the ability of inducing magnetic flux change in the sensor, thus deteriorating the precision of detecting the revolution.
In order to prevent such phenomenon, the antirusting treatment may also be applied to the surface of the rotating ring, but such solution will significantly raise the production cost. Also, dimensional error, if present on the mounting surface of the rotating ring or on the fitting surface of the pulser gear, will hinder adequate mounting of the two. However, an improved precision of working, if employed for preventing such dimensional error, will also raise the production cost.